The present invention relates to dispensing devices and systems that are used for dispensing and applying particles or granulated material onto the surface of a substrate while the dispenser is moved relative to the substrate. In particular, the present invention relates to particle dispensers to be mounted to a vehicle so that during movement of the vehicle particles can be dispensed through the dispenser nozzle onto the surface of road pavement, such as to enhance pavement markings with retroreflective particles.
Pavement marking or striping is typically conducted by applying paints, resins, tapes or the like to the road surface by relative movement of a vehicle with respect to the road surface. That is, markings or stripes are applied over a pavement surface in the direction of movement of such a vehicle. Typical paint or resin application systems comprise spray devices, other contact painting devices, such as rollers or brushes or resin extruders. Tapes are typically provided by unwinding tape from a source roll and applying it to the pavement by way of an application roller. In any case, paint, resin or tape is to be supplied to the dispensing point and applied to the pavement surface in a controlled manner so that the proper amount of paint, resin or tape is provided based upon the demands of usage and required coverage.
In addition to any of the above materials utilized for providing markings or stripes, pavement markings now widely use reflective particles as well. Such paints, resins (e.g. thermoplastics or epoxies) and tapes may contain reflective particles, such as transparent microspheres within their composition. Preferably, the resultant pavement markings are retroreflective so that motor vehicle drivers can vividly see the markings at nighttime. Retroreflective pavement markings have the ability to return a substantial portion of incident light toward the source from which the light originated. Light from motor vehicle headlamps is returned toward the vehicle to illuminate road features, e.g., the boundaries of the traffic lanes, for the motor vehicle driver.
More recent development of optical elements for retroreflective pavement markings are directed to optical elements with greater retroreflectivity at low angles of incidence. Transparent optical elements, such as glass beads, on the one hand each act as a spherical lens so that incident light can be reflected back to the motorist after it passes through an optical element and strikes pigment particles within the marking material. An example of a specialized glass microsphere is described in U.S. Pat. No. 5,853,851.
To reflect more incident light back to the motorist for improved marking visibility, reflective vertical surfaces are being incorporated into pavement markings. For example, raised pavement markers may be provided at intervals along a pavement marking line, such as disclosed in U.S. Pat. Nos. 3,292,507 and 4,875,798. Another example is the use of embossed pavement marking tapes such as disclosed in U.S. Pat. Nos. 4,388,359, 4,069,281, and 5,417,515. Yet other examples comprise the provision of composite retroreflective elements or aggregates that typically include a core material with any number of optical elements embedded to the core surface. Such composite elements may be irregular in shape or may be shaped into spheres, tetrahedrons, discs, square tiles, etc. Such composite retroreflective elements are advantageous because they can be embedded into inexpensive paints and resins. Such composite retroreflective elements are known to comprise polymeric and/or ceramic core compositions. An example of durable retroreflective elements comprising a ceramic core can be found in U.S. Pat. No. 5,774,265. A retroreflective element comprising a multi-sided retroreflector and a clear thermoplastic resin is described in U.S. Pat. No. 5,835,271. Each of the above-noted U.S. patents is fully incorporated herein by reference.
Whether or not the retroreflective optical elements utilized in a pavement markings comprise conventional glass beads or composite optical particles, such optical elements can be incorporated into the pavement marking either as part of the composition of the material that is applied as the pavement marking or they may be dispensed onto the pavement marking material after it is applied but while it is capable of permitting particles to at least partially embed therein, i.e. while the marking material is still sufficiently tacky, wet or soft. In the case of a tape, the optical elements are typically formed into the tape during the tape-making process. But, with paints and resins, optical elements can be mixed into the paint or resin before application, mixed with the paint or resin just prior to application, or dispensed onto the pavement marking material after it has been applied to the pavement surface. Of these, the latter technique is generally preferred because the optical elements are assured of being present at the surface of the pavement marking where their retroreflectivity is functional. Particles within the thickness of the marking may be subsequently utilized after the pavement marking wears down. Also, optical elements dispersed within a paint or resin before or during application may not be retroreflective at all, depending on the transmissivity of the paint or resin, and on whether the entire element is coated with that paint or resin.
Examples of pavement marking painting and bead dispensing systems are described in U.S. Pat. Nos. 4,319,717, 4,518,121, 5,203,923, and 5,294,798. In each of these, the bead dispenser is located on a movable vehicle that also carries the paint or resin applicator, so that an appropriate quantity of beads are dispensed onto the width of the marking in accordance with predetermined marking characteristics. Of these, the device disclosed in U.S. Pat. No. 4,518,121 is directed to a bead dispenser whereby optical beads are deflected into the paint spray so that paint and beads are deposited together on a pavement surface to form a reflective stripe. The others are directed to bead dispensers that apply the beads to the marking paint or resin after it is applied to the pavement surface while still sufficiently wet. Moreover, in these bead applicators that spray beads onto the marking material, the beads are directed from a dispensing unit comprising a nozzle in a downward direction aimed toward the pavement. In U.S. Pat. No. 4,319,717, the disclosed spray gun includes an air nozzle for increasing the impact of the beads to the marking material than would be experienced under gravity alone. The dispensers described in U.S. Pat. Nos. 5,203,923 and 5,294, 798 are described as having the ability to dispense the tiny beads under air pressure through the dispensing valve. That is, the beads are supplied to the dispenser by virtue of a volume of air under pressure that not only moves the beads to the dispenser, but also causes the beads to be dispensed at a higher exit velocity than if simply dropped under the force of gravity.
Other dispensers, including nozzles oriented other than directly toward the pavement surface, are also known. For example, a dispensing nozzle connectable to a pressurized supply of beads is known that includes a plate for directing the beads in an opposite direction as the direction of movement of the vehicle utilized in applying the marking material and the glass beads.
A disadvantage of all of these prior art dispensers and nozzles is that the beads are dispensed onto the pavement marking material at a relative velocity compared to the pavement marking. Where the beads are dropped directly onto the pavement marking, the relative velocity equals the velocity at which the vehicle, whether manual or motor driven, is moving over the pavement. Where the dispensing nozzle faces in the opposite direction than the direction of movement, the relative velocity can be reduced. This depends on whether the beads exit the nozzle with any component of movement in a direction opposite to the direction of travel. This oppositely directed component of movement and thus the amount of reduction of the relative velocity are dependent in these prior art systems upon the pressure by which the glass beads are supplied to the dispensing nozzle.
As discovered in the development of the present invention, the relative velocity at which the optical elements strike the pavement marking material can cause the optical elements to roll along the pavement marking material in the direction of vehicle travel after initial striking. As the elements roll, they pick up some of the paint or resin onto their surface, which prevents that portion of the optical element from retroreflecting light. This phenomenon was discovered and can be quantified by directionally measuring the retroreflectivity of the pavement marking after the optical elements are applied. That is, by comparing the retroreflectivity attained in a direction of a pavement marking facing the direction of movement of the applying vehicle versus the direction from which the vehicle came, the effect of the rolling can be quantified. The greater the difference between the two measured readings, the greater the distance that the element is believed to have rolled, up to the point where the optical elements have rolled through 90 degrees. That is, a 90-degree roll of all of the optical elements would block retroreflectivity from one direction, while from the other direction, retroreflectivity would be substantially unimpaired. Where the two measurements are substantially equal, no significant rolling is believed to have occurred.
This rolling problem can be exacerbated when trying to apply the much larger optical particles, such as the composite retroreflective elements described above. These composite elements can be of many different sizes, but generally, all are significantly greater in volume and mass than typical glass beads, meaning that they each have more momentum when they are dispersed onto the marking material. Rolling of these composite particles within the pavement marking material, like the glass beads discussed above, causes the composite elements to pick up some of the marking material and can block some of its reflective surfaces. This could block the incident light to or through the core material of the composite element, or may shield the reflective nature of a reflective component at the surface of the composite element. Since these larger and more massive retroreflective elements (whether spherical or irregularly shaped) are more likely to roll under a given application condition than glass beads, these composite retroreflective elements may experience rolling and worsened retroreflectivity even where glass beads can be applied with little or no rolling problem.
In this industry, there is a continual desire to apply the pavement markings at greater speeds so as to reduce disruption to traffic conditions and to improve the application process. As can be understood from the above, greater speeds worsen the problem of particle rolling. Even in the case where a nozzle of a dispenser for the particles is directed away from the direction of travel of the vehicle, supplying the particles under pressure to reduce the relative velocity between the particles and the pavement is inadequate. Increasing the supply pressure of the particles to the nozzle in order to propel the particles from the nozzle at a greater velocity, and thus reduce the relative velocity between the particles and the pavement, does not provide satisfactory results because the increased pressure supply also results in an increase of the quantity of the particles supplied through the nozzle. This leads to an increased density of particles applied to a particular pavement marking, which may waste a significant quantity of such particles beyond that which is desired or functional. Regarding the functionality of such particles, it is noted that with the larger composite retroreflective particles, a maximum loading is usually discernable. That is, beyond a predetermined density of particle loading, more particles can actually have a deleterious effect. In particular, the particles may actually shadow one another, thus reducing the retroreflective functionality of the pavement marking.
The present invention is based in part on the discovery of the above-described optical element rolling phenomenon and the recognition of the deficiencies in the prior art. Moreover, the present invention overcomes the disadvantages and shortcomings of the prior art devices for dispensing optical elements onto pavement marking material by providing a fluid-assisted particle dispenser and method for controlling the velocity that the optical elements exit the dispenser to thereby control the relative velocity at which the optical elements strike the pavement marking material when used on a moving vehicle. The fluid assist is advantageously introduced into the dispenser independently of the feed rate of optical elements through the dispenser. That is, the quantity of optical elements to be applied can be controlled independently of the velocity at which the optical elements are to exit the nozzle of the dispenser.
When mounted to a vehicle, a dispenser in accordance with the present invention ejects such optical elements so that they have a velocity component in the opposite direction of movement of the vehicle to which the dispenser is attached. Preferably, the fluid assist causes the optical elements to be ejected from the dispenser nozzle at a velocity to substantially match the forward velocity of the vehicle to which the dispenser is attached. Thus, in accordance with one specific aspect of the present invention, optical elements can be laid down upon marking material that has been applied to a pavement surface at a substantially reduced relative velocity in the direction of extension of the pavement. Preferably the optical elements can be ejected at a component velocity that is substantially the same velocity that the vehicle is moving forward but in the opposite direction so that the relative velocity in the direction of extension of the pavement between the optical elements and the pavement marking material on a road surface is zero. That is, the movement of the optical elements in the direction parallel to the pavement surface rearward (regardless of the component of movement toward the pavement) is preferably equal to the velocity of the vehicle moving forward. By more closely matching the optical element velocity (in a direction opposite the vehicle movement) to the velocity of the vehicle, the optical elements can be laid down without substantial roll along the pavement marking material as applied to a roadway.
This can be accomplished regardless of the size or mass of the optical elements. The result is that the retroreflectivity of the pavement marking is not compromised or negatively affected in either direction (i.e. in the direction of vehicle travel or in the opposite direction). Moreover, the optical elements can be deposited onto the pavement marking material at whatever density is desired to achieve the desired retroreflective characteristic of the pavement marking. This density of application is determined independently of the velocity control caused by the fluid assist. It is also preferable that the dispensing nozzle include a diverging guide surface and have the capability to adjustably control the distribution width so that the optical elements can be applied at a desired width relative to the width of the pavement marking material.
The aforementioned advantages of the present invention are achieved by a particle dispensing device that is to be mounted to a vehicle for use in dispensing optical elements while the vehicle is moving onto pavement marking material that has been applied to a surface as part of a pavement marking process, where the particle dispensing device includes a nozzle, a feed tube and a fluid assist system. The term xe2x80x9cfluidxe2x80x9d as used within the meaning of xe2x80x9cfluid assist systemxe2x80x9d and throughout this application is meant to include liquids and/or gases that are usable as a pressurized source (although not necessarily compressible) and that may be used to propel particles, such as optical elements, in accordance with the present invention. Gases are preferably used because they would not mix within the dispensed particle stream and be applied to the pavement marking material. Air is most preferably used for this purpose.
The nozzle defines an expansion chamber and preferably has a bottom guide plate and a top plate spaced from the bottom guide plate by at least one side wall, the side wall, bottom guide plate providing a guide surface and the top plate to form the expansion chamber with an open side. The bottom guide plate also preferably extends beyond the open side of the expansion chamber to guide particles along the nozzle as they are ejected from the expansion chamber. The particle feed tube is for connection with an optical element supply and connection with the nozzle, the particle feed tube also including an internal passage that opens into the expansion chamber. The fluid assist system comprises an orifice defining element for connection to a pressurized fluid source, the orifice defining element also being operatively connected to the nozzle and positioned to permit fluid under pressure to flow through an orifice thereof and to be injected into the expansion chamber so as to generate the velocity of the particles in the opposite direction of the moving vehicle to which this dispenser is attached. Preferably, the fluid is also injected into the expansion chamber so as to uniformly distribute the particles for dispensing them from the nozzle. Moreover, the guide surface of the bottom guide plate is oriented at least partially horizontally. Most preferably, the guide surface of the bottom guide plate is oriented at approximately 5 degrees to 10 degrees below a horizontal plane (i.e. with the distal end thereof lower than the expansion chamber. The exit particle velocity in the opposite direction of vehicle travel is thus greater than it would be if the particles were to exit under the force of gravity alone.
Preferably, the fluid assist system further comprises a fluid pressure supply line connected to the orifice defining element and connectable to a pressurized fluid source and the orifice defining element includes an internal chamber that has a larger open area in transverse cross section than the orifice thereof, the internal chamber also being open from a side thereof that is connected to the fluid pressure supply line. A surface feature can also be provided at a side of the orifice defining element that is positioned within the expansion chamber, and which surface feature modifies the fluid flow from the orifice into the expansion chamber. The particle dispensing device may also include at least one adjustable side guide element that also extends in the direction of the bottom guide plate from the expansion chamber so as to laterally limit the flow of particles from the nozzle and to guide the particles from the nozzle. The bottom guide plate also preferably diverges from the opening of the expansion chamber.
The aforementioned advantages of the present invention are also achieved by a method for dispensing optical elements onto pavement marking material that has been applied to a pavement surface as part of a pavement marking process from a particle dispensing system of the type having an optical element supply container, a pressurized fluid source and a particle dispensing device that are supported on a movable vehicle, the particle dispensing device including a nozzle having an expansion chamber. Preferably, the expansion chamber is bounded at least in part by top and bottom guide plates that are spaced from one another by at least one side wall and having an open side, the nozzle further being connected to the optical element supply container by way of a feed tube that opens into the expansion chamber of the nozzle and being connected to the pressurized fluid source by way of a fluid assist system having an orifice that also opens into the expansion chamber. A method in accordance with the present invention is characterized by including the steps of orienting the dispensing device so that the guide surface of the bottom guide plate of the nozzle is at least partially extended in the direction of extension of the pavement surface to which optical elements are to be applied; feeding optical elements to the expansion chamber of the nozzle while the vehicle is moving; and supplying pressurized fluid through the orifice of the fluid assist system and into the expansion chamber of the nozzle while optical elements are also fed into the expansion chamber and thereby generating a controlled component velocity of the particle flow from the nozzle in the opposite direction of the direction of vehicle velocity to which this dispenser is attached.
A method in accordance with the present invention is also preferably characterized by conducting the orienting step so as to orient the open side of the expansion chamber in a direction opposite to the direction of vehicle travel and to orient the nozzle so that its bottom guide plate extends moreso in the direction of extension of the pavement surface to which optical elements are to be applied than in a direction directly toward the pavement surface to which optical elements are applied. The step of feeding optical elements can be done under pressure to thereby urge the optical elements toward the expansion chamber. Preferably, the step of supplying pressurized fluid further comprises supplying pressurized air, which air pressure can be independently controlled so that the air pressure and air flow through the orifice into the expansion chamber ejects the optical elements from the nozzle at an exit velocity that is based upon a desired relative velocity of the optical elements to the surface of the pavement to which the optical elements are to be applied. Most preferably, this step comprises substantially matching a component of the particle exit velocity in the rearward direction of vehicle movement (i.e. the direction of extension of the surface of the pavement to which the optical elements are to be applied) with the velocity of the vehicle and thereby substantially causing a zero relative velocity between the optical elements and the surface of the pavement in the direction of its extension. The method may also comprise a step of laterally guiding the optical elements from the expansion chamber of the nozzle by at least one adjustable side guide element that is operatively supported and positionable at multiple locations with respect to a diverging side edge of the bottom guide plate. Moreover the method is preferably utilized with the additional step of applying the optical elements in accordance with a desired optical element density onto pavement marking material that has been previously applied to a pavement surface as part of a pavement marking process while it is capable of at least permitting optical elements to embed within the marking material.